Allow color specification on Asset3D

[EtaLoop]

What

The idea is to reproduce behavior of Mesh3D regarding color modification on Asset3D :

• add albedo_factor
• add vertex_colors as in Mesh3D

In order to overwrite white default texture of Asset3D loaded from stl and obj (gltf already have albedo_factor in file).

See: #5253

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[Wumpf]

Thanks for your contribution!! 🙂

AlbedoFactor makes a lot of sense to me since this can be applied on all mesh/model formats, would love to get this in. But I don't see yet how we can add vertex_colors in a tractable & defined way. However, maybe we can come up with some rule for it?
Very relatedly, we have to keep in mind that more model formats may be added in the future and we need to avoid ugly surprises in that context. Therefore, I think all additional properties on Assed3D should be "postprocesses" on the loaded mesh. This makes it more robust against future formats and makes it a lot easier to specify what they do.

[Wumpf]

let me know when you think this is ready for review again! :)
(or use the little "re-request review" button so this shows up in my review queue again)